Does Exclusive Consumption of Plant-based Dietary Protein Impair Resistance Training-induced Muscle Adaptations?

Abstract

Dietary protein consumption maximizes the anabolic response during resistance training (RT) by triggering muscle protein synthesis and providing the indispensable amino acids for a net positive protein balance. Leucine is considered the key amino acid in this process, suggesting that differences in protein quality may influence RT-induced gains in muscle mass and strength. In this respect, despite acute evidence on lower anabolic properties of plant- vs. animal-based protein, the effects of an exclusive plant-based dietary protein diet on RT-induced adaptations are currently unknown. PURPOSE: To investigate the impact of dietary protein source (plant- vs. mixed diet-based protein) on RT-induced changes in muscle mass and strength in total protein-matched young healthy men. METHODS: Nineteen vegan (VEG 26±5 y; 72.7±7.1 kg, 1.78±0.05 m) and nineteen omnivorous (OMN 26±4 y; 73.3±7.8 kg, 1.76±0.06 m) physically active young men were enrolled in a 12-week, twice weekly, lower-limb RT program. Daily protein intake was adjusted to 1.6g/kg/day in both groups via supplementing either soy (VEG) or whey (OMN) protein. Leg lean mass (LLM, by DXA) and lower-limb maximal strength (leg-press one-repetition-maximum, 1-RM) were determined PRE and POST intervention. Six 24-hour dietary recalls were performed at baseline (for habitual protein intake determination) and three during the intervention, for monitoring purposes. RESULTS: Significant increases in LLM were observed in both VEG (PRE=18.9±2.2 kg and POST=20.1±2.2 kg, ∆%=6.4±5.8 %, p<0.0001) and OMN (PRE=19.1±2.4 kg and POST=20.3±2.7 kg, ∆%=6.1±3.9 %, p<0.0001). Similarly, 1-RM was significantly increased in both VEG (PRE=258±59 kg and POST=354±81 kg, ∆%=38.1±15.9 %, p<0.0001) and OMN (PRE=261±63 kg and POST=381±73 kg, ∆%=49.0±21.6 %, p<0.0001). No group by time interactions were found. Finally, total protein intake was similar between groups (VEG=1.68±0.14g/kg/d and OMN=1.72±0.10g/kg/d, p=0.30). CONCLUSION: A higher protein-content (~1.6g/kg/day) exclusive plant-based (including soy) protein diet is similarly effective as a mixed-diet in supporting RT-induced muscle adaptations, suggesting that total protein, rather than protein quality, may be more important for muscle adaptation in young individuals. Supported by FAPESP grant 2016/22083-3.